Device and Method for Packaging Dry Ice in a Plastic Film

ABSTRACT

The present invention relates to a method and device for packaging dry ice in a plastic film, the said device comprising: —means for dispensing and shaping a plastic film comprising a shaping sleeve over the exterior wall of which the plastic film is paid out, —a dry ice generator connected to a source of liquid carbon dioxide, the dry ice generator being positioned inside the shaping sleeve so as to leave a gap between the generator and the shaping sleeve and allow the plastic film shaped to become filled with dry ice, —and means for sealing the shaped plastic film, characterized in that the shaping sleeve is equipped with thermal insulating means and/or with heating means.

The present invention relates to a device for packaging dry ice in the form of carbon dioxide snow in a plastic film. The invention also relates to a method of packaging carbon dioxide snow in plastic bags in a continuous and automatic manner, using said device.

It is known that frozen, deep-frozen or else fresh products, in particular food products, which have to be maintained at a controlled temperature of +6° C. to −20° C. or less, without interruption of their cold chain from the time they are cooled, frozen or deep-frozen until the time of their use, require warehouses, means of transport and shops provided with refrigeration equipment, which at the present time is generally electrical. However, in many situations, for example in the case of non-motorized transportation, it is impossible to transport the products without taking them out of the refrigeration equipment in which they are stored, since the risks of a rise in temperature are considerable, particularly if the climate conditions are unfavorable. In order to avoid such a rise in temperature during their transportation, it is common practice to place the fresh, frozen or deep-frozen products in an environment maintained at a controlled temperature in an isothermal enclosure. The temperature is regulated, for example, by the slow sublimation of carbon dioxide snow packed into perforated plastic film bags. Carbon dioxide snow is a relatively inexpensive product and has a cooling capacity. Its temperature of approximately −80° C. allows the products to be kept cold for a relatively long time.

Thus, application EP 1 186 842 describes a device for packaging carbon dioxide snow in a plastic film, comprising means for dispensing and shaping the plastic film, a carbon dioxide snow generator in the form of a tube connected to a source of liquid carbon dioxide and placed in such a way as to fill the shaped plastic film. The means for dispensing and shaping the plastic film comprise a shaping sleeve for the plastic film that is placed concentrically around the carbon dioxide snow generator while leaving a free space between the shaping sleeve and the carbon dioxide snow generator. When the pressurized liquid carbon dioxide is released at the upper part of the carbon dioxide snow generator, it expands to atmospheric pressure and strikes the walls of the carbon dioxide snow generator, thus leading not only to the formation of a solid in powdery form, known by the name of carbon dioxide snow, at a temperature greatly below 0° C., of around −80° C., but also to the formation of carbon dioxide in the gaseous state, likewise at a temperature greatly below 0° C., of around −80° C. The carbon dioxide snow thus obtained drops under gravity into the shaped plastic film, while the gaseous carbon dioxide escapes through the space formed between the shaping sleeve and the carbon dioxide snow generator.

However, this device has a major disadvantage which prevents it from being used continuously on an industrial scale. This is because the gaseous carbon dioxide which escapes into the space formed between the carbon dioxide snow generator and the shaping sleeve significantly cools the walls of the shaping sleeve, causing a sudden cooling of the water vapor present in the ambient air, with the resultant formation of ice crystals on the walls, particularly the outer walls, of the shaping sleeve. The formation of ice crystals prevents the plastic film from advancing along the shaping sleeve. As the moisture level in the ambient air increases, this phenomenon becomes more pronounced.

The objective of the present invention is therefore to overcome all or some of the disadvantages of the prior art device.

Accordingly, the invention relates to a device for packaging carbon dioxide snow in a plastic film, comprising:

-   -   means for dispensing and shaping a plastic film that comprise a         shaping sleeve along whose outer wall the plastic film is         unwound,     -   a carbon dioxide snow generator connected to a source of liquid         carbon dioxide, the carbon dioxide snow generator being placed         inside the shaping sleeve so as to leave a free space between         the generator and the shaping sleeve and allow the shaped         plastic film to be filled with carbon dioxide snow, and     -   means for sealing the shaped plastic film, characterized in that         the shaping sleeve is equipped with thermal insulating means         and/or heating means.

By equipping the shaping sleeve with thermal insulating means and/or heating means, the gaseous carbon dioxide, which is formed during the generation of carbon dioxide snow, is prevented from suddenly cooling the walls of the shaping sleeve. It is thus possible to avoid the formation of ice crystals on the walls, particularly the outer walls, of the shaping sleeve. Consequently, the plastic film no longer sticks to the shaping sleeve and there are no longer any problems with advancing the plastic film due to the cooling of the walls of the shaping sleeve by the gaseous carbon dioxide formed during the generation of carbon dioxide snow.

Other features and advantages of the invention will become apparent on reading the description which follows. Forms and embodiments of the invention are given by way of non-limiting examples illustrated by the appended drawings, in which:

FIG. 1 is a schematic view of a device according to the invention;

FIG. 2 is a schematic view of a bagging device;

FIG. 3 is a detail of the device shown in FIG. 1;

FIG. 4 is a detail of one particular embodiment of the invention;

FIG. 5 is a cross section taken on AA′ in FIG. 4.

The insulating and/or heating means with which the shaping sleeve is equipped are such that they allow the surface of the wall of the shaping sleeve along which the plastic film is unwound to be maintained at a sufficiently high temperature to avoid any crystallization of the water vapor on this wall. Advantageously, this temperature is at least −10° C., preferably at least 0° C., and more preferably still at least 10° C.

In one particular embodiment, the thermal insulating means can consist of at least one layer of insulating material selected from the group consisting of cork, polystyrene, glass wool, etc. The layer of insulating material can be applied to the inner surface of the shaping sleeve, that is to say to that surface of the shaping sleeve opposed to the surface along which the plastic film slides. Given that this layer is in contact with the carbon dioxide gas, it is preferably not porous and can optionally be covered with a thin layer or protective skin made of a non-porous material which is preferably insulating as well.

The skin can consist, for example, of a metal or plastic film.

According to another embodiment, a free or empty space is formed between the layer of insulating material and the inner surface of the shaping sleeve. The free space is a space devoid of material and filled with ambient air at atmospheric pressure, or else placed under a vacuum.

According to one particular embodiment, the inner surface of the shaping sleeve comprises, instead of the layer of insulating material or juxtaposed with the layer of insulating material, at least one layer of heating material.

The layer of heating material consists, for example, of an electrical resistor, or else of a hollow element filled with liquid whose temperature can be adjusted (for example eutectic).

In the free space can be placed a temperature sensor so that the temperature of the layer of heating material can be adjusted to the desired temperature.

According to one particularly advantageous embodiment, the inner wall of the shaping sleeve consists of a superposed arrangement of layers of heating and insulating materials which can be juxtaposed or separated by at least one empty region.

Thus, a particularly appropriate superposed arrangement consists of the successive arrangement of a protective skin, a layer of insulating material, a layer of heating material and an empty space, it being possible for the empty space to be provided with a heat sensor, the empty space being situated closest to the inner wall of the shaping sleeve.

A person skilled in the art will be able to adapt the number, nature and thickness of the constituent layers to suit the capacities of the machine and the desired production rate.

By way of illustration, possible thickness ranges can be as follows:

-   -   protective skin: 0.5 mm to 5 mm, preferably 0.8 mm to 2 mm;     -   insulating material: 0.5 cm to 10 cm, preferably 2 cm to 5 cm;     -   heating material: 2 cm to 15 cm, preferably 3 cm to 10 cm;     -   empty space: 1 cm to 5 cm, preferably 2 cm to 4 cm;         the wall of the shaping sleeve having a thickness of between 0.5         cm and 3 cm, preferably of around 1 cm.

Advantageously, the device for packaging carbon dioxide snow comprises means for injecting inerting gas in the region of the carbon dioxide generator. This makes it possible to continuously flush the carbon dioxide snow generator in order to prevent air or carbon dioxide entraining carbon dioxide snow from being sucked back into the carbon dioxide snow generator when the supply of liquid carbon dioxide is interrupted and in order to allow improved dropping of the carbon dioxide snow into the shaped plastic film.

The means for injecting inerting gas comprise, for example, a gas feed nozzle arranged at the inlet of the carbon dioxide generator.

The inerting gas used can be any gas which is not reactive with respect to the carbon dioxide snow. If the carbon dioxide snow is intended for preserving food products, this gas will be compatible with such a use. The preferred gas is carbon dioxide. However, preference is given above all to using a substantially anhydrous inerting gas (dew point of around −40° C.) in order, given the temperature of the carbon dioxide snow, to prevent any traces of water from icing to form water ice.

According to one particular embodiment, the device for packaging carbon dioxide snow can comprise means for injecting a fluid having a temperature below the dew point temperature of air into contact with and inside the plastic film container. For example, such means can consist of an injection rod which is arranged in the space formed between the carbon dioxide snow generator and the shaper and whose free end is oriented toward the plastic film released by the shaper.

Any food-quality fluid is suitable for this purpose. However, liquid carbon dioxide is preferred.

According to one particular embodiment, the means for injecting liquid carbon dioxide is connected to the source of liquid carbon dioxide which is used to generate carbon dioxide snow. A valve, generally a solenoid valve, is inserted between the injection rod and the source of liquid carbon dioxide so as to start and stop the supply of liquid carbon dioxide. A valve, generally a solenoid valve, is also inserted between the carbon dioxide snow generator and the source of liquid carbon dioxide so as to start and stop the supply of carbon dioxide snow. When the device according to the invention is switched on, the solenoid valve of the capillary injection rod is open, then closed, before the solenoid valve of the carbon dioxide snow generator is opened. The valves can be controlled by a timer determining how long they remain open and hence the amount of carbon dioxide snow to be packaged. The timer can be started by any means, including a coin-operated system.

According to one advantageous embodiment, the device for packaging carbon dioxide snow comprises at least one means for removing the gaseous carbon dioxide. This means can consist of the space formed between the outer wall of the carbon dioxide snow generator and the inner wall of the shaping sleeve. The removal means is connected at its top to a containment box, which will be connected, on the one hand, to an adjustable “hot” air inlet for heating this carbon dioxide gas, which is at a temperature of around −80° C., and on the other hand to a line which is itself connected to a vacuum system used to suck in this toxic mixture.

The means for dispensing, shaping and moving the plastic film are those conventionally employed in known packaging devices. Generally, these means consist in continuously dispensing a strip of plastic film, in shaping it into a tube by winding it around a preshaping sleeve, in sealing the two edges of the tube which meet, and in sliding the tube obtained downstream of the preshaping sleeve. The means for sealing the plastic film, once said film has been shaped, make it possible to close the tube by thermal welding and then to cut it at the welded film stage in order to obtain a bag. In this case, the carbon dioxide snow generator is placed inside the shaping sleeve in such a way that the snow produced is directed into the bag being formed. Preferably, the means for dispensing and shaping the plastic film are positioned in such a way as to form a vertical bag whose opening is on the top side, and the carbon dioxide snow generator is oriented vertically in such a way that the carbon dioxide snow formed drops under gravity into the shaped plastic bag and in such a way that, once the latter has been sealed and cut, the bag containing the carbon dioxide snow also drops under gravity.

The plastic film is generally chosen from materials allowing evacuation of the gaseous carbon dioxide resulting from the sublimation of the carbon dioxide snow. This property can be achieved by the porosity of the plastic film. The plastic film used is then microporous or has microperforations. Thus, the plastic film can be chosen such that the perforations make it possible for the significant mass of expansion gas to escape and also for the fine crystals making up the carbon dioxide snow to be retained and contained. The microperforations can be produced at the time of manufacturing the plastic film or during the method according to the invention, for example in a prior step of preparing the plastic film such as by passing the plastic film over perforating spikes. Preferably, the plastic film can be thermally welded. It is also preferable, on the one hand, for it to be strong enough to withstand the pressure of the carbon dioxide snow while it is being filled and handled, and, on the other hand, for it to be sufficiently thermally insulating to avoid any risk of cold burns when it is being handled; these two properties can be obtained by choosing a sufficiently large thickness of material. Furthermore, if the container is intended for use in the food industry, the material chosen must of course be suitable for this use. Finally, it is generally preferable for the plastic film to be biodegradable in order to respect the environment. According to the preferred implementation of the invention, the plastic film is microperforated polypropylene having a thickness of between 25 and 80 microns, preferably between 35 and 70 microns.

Of course, the thickness of the plastic film will be tailored to the quantity of carbon dioxide snow contained in a bag. In the same way, the number of perforations and their diameter will be tailored to suit the quantity of carbon dioxide snow contained and the desired rate of sublimation.

The device can also comprise at least one means for compacting the carbon dioxide snow in the plastic film container. Such a means can consist of a tamper arranged on the lower part of the plastic film container. Said tamper can be actuated by a system of electromagnets or by an electropneumatic system.

The invention also relates to a method of packaging carbon dioxide snow in a plastic film container, wherein:

-   -   carbon dioxide snow is generated in a carbon dioxide snow         generator by injecting liquid carbon dioxide,     -   the carbon dioxide snow formed is introduced into a plastic film         container, and     -   the plastic film container is closed, characterized in that an         inerting gas is continuously injected into the carbon dioxide         snow generator.

As mentioned above in relation to the device for packaging carbon dioxide snow according to the invention, the injection of an inerting gas into the carbon dioxide snow generator makes it possible to continuously flush the carbon dioxide snow generator in order to prevent air or carbon dioxide from being sucked back into the carbon dioxide snow generator when the vaporization is stopped and to allow improved dropping of the carbon dioxide snow into the shaped plastic film.

Any gas which does not react with the carbon dioxide snow is suitable for this purpose. Of course, if the carbon dioxide snow is intended for a food use, the gas used will be of food quality. Preferably, carbon dioxide is used.

The injection of carbon dioxide into the carbon dioxide snow generator takes place in a pulsed manner, that is to say that the vaporization is stopped as soon as a sufficient quantity of liquid carbon dioxide has been injected to give the desired quantity of carbon dioxide snow.

The method can additionally comprise a step of forming a plastic film container. This step allows the continuous formation of an open plastic film container. The carbon dioxide snow formed is then introduced into said container through its opening and then the opening is closed, for example, by heat sealing.

Advantageously, the plastic film container is formed using a packaging device comprising a preferably cylindrical shaping sleeve which is arranged vertically and whose operation has been described above in connection with the device. The carbon dioxide snow formed fills the container under gravity and then, when the desired quantity of carbon dioxide snow has been introduced, the upper part of the container is sealed.

According to one particularly advantageous embodiment of the method of the invention, a continuous additional step of maintaining the temperature of the shaping sleeve is added. In this step, the temperature of the shaping sleeve is maintained at a temperature of at least −10° C., preferably at least 0° C., and more preferably still at least 10° C.

The method according to the invention can also comprise a step of continuously removing the gaseous carbon dioxide formed during the step of carbon dioxide snow formation. The gaseous carbon dioxide removed along the carbon dioxide snow generator is generally discharged away from the premises in which the carbon dioxide snow is packaged, for safety reasons.

Another optional step of the method according to the invention comprises injecting a fluid having a temperature below the dew point temperature of air into contact with and inside the plastic film container prior to injecting liquid carbon dioxide.

According to the preferred embodiment of the invention, the fluid having a temperature below the dew point temperature of air is liquid carbon dioxide. Thus, during the step of carbon dioxide snow formation, or prior to this step, it is sufficient to inject a small quantity of liquid carbon dioxide so as to cool the inner wall of the plastic film container to a temperature below the dew point temperature of air. Generally, a few grams of liquid carbon dioxide at −80° C. or a squirt of the latter from a capillary is sufficient. This step can be carried out at each new step of carbon dioxide snow formation or else only when starting up the device after a prolonged shutdown.

At the end of the filling step, the method can comprise a compacting step which makes it possible to compact the carbon dioxide snow in the container in order to facilitate sealing of the upper part of the container.

According to one preferred embodiment of the invention, the method is a continuous carbon dioxide snow packaging method.

Generally, the liquid carbon dioxide which is injected inside and into contact with the plastic film container and that which is injected into the carbon dioxide snow generator come from the same source of liquid carbon dioxide. The carbon dioxide source can be a cylinder of pressurized carbon dioxide in the liquid state, but it is preferably rather a source of refrigerated low-pressure liquid carbon dioxide since this type of source leads to better efficiency in terms of carbon dioxide snow generation. In this second case, the conditions under which the source of liquid carbon dioxide is stored can, for example, be a temperature of −20° C. and a pressure of approximately 20 bar, or even less.

FIGS. 1 to 5 illustrate the device and the method according to the invention. The complete system (1) is represented in FIG. 1. The device (2) according to the invention is supplied with liquid carbon dioxide contained in a refrigerated reservoir (3) of liquid carbon dioxide via a lagged pipe (4) and a lagged hose (5). Filters (6 a and 6 b) and shutoff valves (7, 8) can be placed between the carbon dioxide source (3) and the generator (2), it being possible in particular for one (8) of these valves to be placed between the pipe and the hose. The lagged pipe can be provided with an orifice (9) connected to a shutoff solenoid valve (10) leading to a degassing pot (11), the lower part of the degassing pot being connected to the lagged pipe (4) by means of a cross-section increasing system (12) allowing the separation of the gas and the liquid. A valve (13) is also present between the stop valve (8) and the production valve (14). After this production valve (14) is mounted an injection nozzle (15). The carbon dioxide snow generator (16) is adjoined by a system (17) for flushing with dry air or gaseous CO₂ at low pressure (a few millibar) maintained by a regulator (18), which can be controlled by a solenoid valve (19).

The carbon dioxide snow generator (16) is placed inside the shaping sleeve (20) of a vertical bagging machine (21) represented in FIG. 2.

When the method is implemented, the plastic film (22) is wound around itself to form a tube which is taken up by the shaping sleeve (20). The film is wound in such a way as to bring the two vertical edges of the film closer together: these edges are made to overlap and are then bonded together by thermal welding with vertical sealing means (23) over their entire length. The tube formed is moved downward by guide pulleys (24) so as to form a plastic bag or container (25) into which carbon dioxide snow can be introduced. In FIG. 2, the arrows indicate the movements of the shaping and sealing means. Once the bag has been formed into shape, the solenoid valve (14) opens for a few tenths of a second: the liquid carbon dioxide comes out and the generator (16) then produces carbon dioxide snow (26), which drops under gravity into the plastic bag (25). The solenoid valve (14) is closed. During all its operations, the carbon dioxide gas is removed from the plastic bag (25). The solenoid valve (14) is closed. The carbon dioxide gas is removed through the space (27) formed between the plastic film shaping sleeve (20) and the carbon dioxide snow generator (16). Finally, the sealing tools (28) of the bagging machine close the plastic by thermal welding and cut the welded plastic to form a closed bag (29).

The device (2) according to the invention is described in more detail in FIGS. 3 to 5, which show the carbon dioxide snow generator (16) arranged inside the shaping sleeve (20) along whose outer wall is unwound the plastic film (22) which is driven by the drive rollers (24). The space (27) formed between the generator (16) and the inner wall of the shaping sleeve, which is covered with an insulating means (28), makes it possible to remove the carbon dioxide formed. The carbon dioxide snow (26) which drops into the plastic film container under gravity is formed by injecting liquid carbon dioxide through the nozzle (15) into the upper part of the generator (16). An inerting gas is injected through the nozzle (17).

The preferred embodiment of the means for insulating and heating the shaping sleeve is illustrated in FIGS. 4 and 5. In this embodiment, the insulating and heating means (28) consist of a superposed arrangement of layers of different materials in the following way. Starting from the inner wall (20 a) of the shaping sleeve (20) are situated an empty space (29), a layer (30) of heating material, a layer of insulating material (31), and a protective skin (32). In the empty space is arranged a heat sensor (33). These figures also show the rod (34) for injecting a fluid whose temperature is below the dew point temperature of air.

By employing a device as described above, it is possible to continuously fill bags of carbon dioxide snow at a rate of 1 minute per bag for bags containing 2 kg of carbon dioxide snow.

No problem is encountered when closing the plastic bag by thermal welding or with regards to continuously unwinding the plastic film, even after a long shutdown of the device. 

1-14. (canceled)
 15. A device for packaging carbon dioxide snow in a plastic film, said device comprising an element adapted to dispense and shape a plastic film that comprises a shaping sleeve along whose outer wall the plastic film is unwound, a carbon dioxide snow generator connected to a source of liquid carbon dioxide, the carbon dioxide snow generator being placed inside the shaping sleeve so as to leave a free space between the generator and the shaping sleeve and allow the shaped plastic film to be filled with carbon dioxide snow, and an element adapted for sealing the shaped plastic film, characterized in that the shaping sleeve is equipped with a layer of thermal insulating material and/or a layer of heating material.
 16. The device for packaging carbon dioxide snow of claim 15, wherein the layer of thermal insulating material and/or layer of heating material are such that they allow the surface of the wall of the shaping sleeve along which the plastic film is unwound to be maintained at a temperature of at least −10° C., preferably at least 0° C., and more preferably still at least 10° C.
 17. The device of claim 15, wherein the layer of thermal insulating material is made of a material selected from the group consisting of cork, polystyrene and glass wool.
 18. The device of claim 17, wherein a free or empty space is formed between the layer of thermal insulating material and the inner surface of the shaping sleeve.
 19. The device of claim 17, wherein the inner surface of the shaping sleeve comprises, instead of the layer of insulating material or juxtaposed with the layer of insulating material, at least one layer of heating material.
 20. The device of claim 15, wherein said layer of thermal insulating material and/or layer of heating material comprises a superposed arrangement of a protective skin, the layer of thermal insulating material, the layer of heating material and an empty space adapted to be provided with a heat sensor, the empty space being situated closest to the inner wall of the shaping sleeve.
 21. The device of claim 15, further comprising: a gas feed nozzle arranged at the inlet of the carbon dioxide generator adapted to inject inerting gas into the carbon dioxide snow generator, and/or an injection rod disposed in the free space having a free end oriented toward the plastic film released by the shaper, said injection rod being adapted to inject a fluid having a temperature below a dew point temperature of air into contact with and inside the plastic film container; and/or at least one tamper for compacting the carbon dioxide snow in the plastic film container.
 22. A method for packaging carbon dioxide snow in a plastic film container, comprising the steps of: generating carbon dioxide snow injecting liquid carbon dioxide into a carbon dioxide snow generator; introducing the carbon dioxide snow into a plastic film container, and closing the plastic film container, wherein a gas is continuously injected into the carbon dioxide snow generator.
 23. The method of packaging carbon dioxide snow of claim 22, further comprising: forming the plastic film container using a packaging device comprising a shaping sleeve.
 24. The method of claim 23, further comprising: maintaining a temperature of the shaping sleeve, preferably at a temperature of at least −10° C.
 25. The method of claim 22, further comprising: continuously removing gaseous carbon dioxide from the plastic film container that is formed during said steps of generating and introducing.
 26. The method of claim 22, further comprising: injecting a fluid having a temperature below a dew point temperature of air into contact with and inside the plastic film container prior to the injection of liquid carbon dioxide.
 27. The method of claim 22, further comprising: compacting the introduced carbon dioxide snow.
 28. The method of claim 22, wherein said method is continuously performed.
 29. The method of claim 15, further comprising an element adapted to remove the gaseous carbon dioxide connected, on one hand, to an adjustable hot air inlet for heating the carbon dioxide gas, and on the other hand to a line which is itself connected to a vacuum system.
 30. The method of claim 21, further comprising an element adapted to remove the gaseous carbon dioxide connected, on one hand, to an adjustable hot air inlet for heating the carbon dioxide gas, and on the other hand to a line which is itself connected to a vacuum system.
 31. The method of claim 22, wherein the continuously injected gas is carbon dioxide.
 32. The method of claim 23, further comprising: maintaining a temperature of the shaping sleeve, preferably at a temperature of at least 0° C.
 33. The method of claim 23, further comprising: maintaining a temperature of the shaping sleeve, preferably at a temperature of at least 10° C. 